They have each been arrested and questioned twice during the 11-month inquiry, as the investigation concentrated at first on cash-for-honours and then on allegations of a cover-up. Downing Street has consistently denied any wrong-doing over the inquiry.

But furious detectives believe the leak was a deliberate attempt to destroy the probe, which is now in its final stages.

A Crown Prosecution Service source said: "We believe the leaks are coming from government sources who are trying to disrupt the inquiry.

"If evidence police are hoping to rely on appears in the media it could bring down the whole case. Those in the firing line are well aware of that."

The move for an injunction also prompted intense speculation that charges could be imminent.

The News of the World has learned that detectives believe they have uncovered clear evidence to bring charges alleging a conspiracy to pervert the course of justice.

He explained: "The important thing to remember is that the Attorney General acts in the public interest and, in particular, he has an interest to ensure that no possible prosecution is prejudiced and no possible defence is prejudiced.

"The inference of Lord Goldsmith's actions was that he at least contemplates the possibility that a prosecution of some kind will follow."

And media lawyer Mark Stephens said: "I would expect a development this weekend. I would be astonished if there wasn't."